Plastic impression compositions

ABSTRACT

NEW PLASTIC COMPOSITIONS ARE DISCLOSED WHICH CAN BE USED FOR TAKING IMPRESSIONS WHILE THE COMPOSITION IS INITS PLASTIC STAGE, SAID COMPOSITION INCLUDING A SOLID RESIN AND A SOLVENT SYSTEM WHICH INCLUDES AN EXTENDER AND A BENZYL RADICAL COMPOUND SUCH AS BENZYL ALCOHOLS, BENZYL ETHERS, BENZYL KETONES, BENZYL ALDEHUDES, AND BENZYL ESTERS. THE SOLVENT SYSTEM LEADS TO A CONTROLLED EARLY SETTING, AND INPARTS IMPROVED PROPERTIES TO THJE PLASTIC COMPOSITION FOR TAKING IMPRESSIONS, PARTICULARLY OF LIVING ANATOMICAL STRUCTURES.

3,558,540 PLASTIC IMPRESSION COMPOSITIONS Eugene J. Molnar, 713 S. StoneAve., La Grange, Ill. 60525 No Drawing. Continuation-impart ofapplication Ser. No.

607,883, Jan. 9, 1967. This application Nov. 13, 1968,

Ser. No. 775,489

Int. Cl. C08f 21/04, 45/34 US. Cl. 260-23 6 Claims ABSTRACT OF THEDISCLOSURE The present invention is in the field of plastic impressioncompositions, particularly plastic compositions used to make anatomicalimpressions for making later reproductions. This application is acontinuation-in-part of copending US. application, Ser. No. 607,883,filed Jan. 9, 1967, now abandoned, and by the same applicant.

The plastic compositions of this invention will be particularly directedto the use of the compositions for taking impressions of the ear. Itshould be understood that such a description and discussion relative tothe ear may likewise be extended to taking other anatomical impressionsor other equivalent uses, for example, mouth impressions, or use asdental issue conditioners and temporary denture liners.

The art has devised methods for taking ear impressions, for example, asparts for hearing aid devices; and the art has generally used thematerials developed in the dental art for taking impressions of themouth. Special techniques and training have been developed in the dentalart for taking dental impressions, and these techniques and training donot successfully meet all the problems in taking ear impressions.Special problems are encountered in taking dental impressions which arenot necessarily the same or may be altogether different in the earimpression art. For example, the dental practitioner never contacts themouth parts which are to be later copied with the impression materialalone. The dental practitioner uses trays or similar devices tointroduce the plastic impression material into the mouth, therefore, theplastic impression material is confined during the impression takingstep. The use of the tray is important for taking mouth impressionsbecause the practitioner is able to evenly distribute the material, andto employ an equalized pressure in the distribution of the impressionmaterial against the parts of the month which will be reproduced. Theseprocedures are required in order to obtain an accurate reproduction ofany part of the mouth.

The average practitioner in the hearing aid field has limited trainingin such impression techniques and limited knowledge of the nature andphysical properties of the impression materials which are required forsuccessful practice.

In the hearing aid field, the plastic impression material is generallyworked into the ear canal and against the outer areas of the ear withthe fingers while in the plastic deformable or mold making stage. Suchplastic impression material is not confined with a tray and,consequently, the pressure on the impression material is not evenly dis-United States Patent Olfice Patented Jan. 26, 1971 tributed. After thepractitioner obtains his ear impression, he generally surrounds it withan investment which is usually a mixture of modified plaster and water.This mixture is allowed to set or harden and] the impression is thenwithdrawn from the mold cavity which has been formed by the investmentmaterial around the impression. The negative mold is then used forreproducing the positive hearing aid or other insert called the earmold, for example.

The dental impression materials now available do not adequately servefor the above purposes for several reasons. These reasons include theproblem of tackiness of the dental impression materials which makes handmanipulation difiicult, and which presents a problem of the plasticimpression material adhering to the dry ear surface. In general, thedental impression materials require more exacting handling techniquesand a greater demand on the training and skill of the practitioner whichis not commonly encountered among practictioners who are not dentallyoriented. A further objection of some of the dental impression materialsfor this use is the problem of the development of exothermic heat whichoccurs during setting of some dental impression materials. Heat islikely to cause discomfort to the subject or even injury to the eartissues. A further disadvantage of using dental impression materialsrelates to the undercuts which exist in the ear. Impressions of suchundercuts are likely to be distorted or fractured when using many of thedental impression materials during the step of withdrawal from the ear.The use of some dental impression materials also results in problemswhen separating the impression from the investment mold.

It will be understood that impression materials which are generally usedfor sensitive areas, such as the ear canal, would desirably enjoy otheradvantages such as the ability to take a quick accurate impression,provide little or no discomfort to the subject, pose no problem ofinfection or physiological incompatibility, and even actively reduce thelikelihood of infection. Such materials should form a non-tacky gelwithin a short time to take an impression, and also set within areasonably short time so that the material may be removed. On the otherhand, they should not set too quickly so as to hamper handling thereof.It is therefore one general object of the invention to provide newplastic compositions which can be successfully used ot take anatomicalimpressions, such as the ear. k

Another object of this invention is a plastic impression taking materialwhich has improved properties to permit practitioners of limitedtraining and skill to successfully take anatomical impressions,particularly impressions of the ear, to make ear molds for hearing aids,medical stethescope ear pieces, sound receiver units for radio,telephone and other transcription reception, swimming ear plugs, noiseblocking ear plugs, and the like.

A still another object of the invention is to provide a plasticcomposition which can be quickly and simply mixed and manipulated whilethe plastic composition goes through its various viscosity stageswithout encountering disadvantages which would present problems inhandling such as a too rapid loss of the impression taking or plasticstages.

In view of the foregoing objects, it is a still further object toprovide a plastic composition for taking impressions in which a highlysuccessful gel forming agent is employed which has controlledevaporation so that undesirable dimensional changes do not occur in theplastic composition, and the tissue is not irritated.

It is a further object to provide a plastic impression composition wherethe gel forming agent has other desirable properties such as low wateradsorption so as not to dehydrate human tissue. Another feature of thisobject is to obtain a plastic impression composition wherein thesuccessful gel forming agent does not present problems of irritation tothe tissue and is not esthetically objectionable with respect to odorsor handling properties.

A still further object of the invention is to provide a plasticcomposition in which a resin is combined with a solvent system whichprovides a mixture having a quick but controlled setting time, saidsolvent system including an extender to provide the desired feature ofcontrolled setting time, as well as providing other desirable featuresand properties.

The foregoing objects are attained together with other objects whichwill occur to practitioners from considering the following disclosure ofthe invention.

The plastic compositions of this invention include a resin which may beany soluble room temperature soluble synthetic resin such as alkylmethacrylates, vinyl acetate and vinyl chloride, copolymers such asvinyl acetate-vinyl chloride, and the like. Various additives may beadded to the solid resin such as pigments for coloring, fillers,modifiers, or the like. The resin is soluble in the sense that a solventsystem successfully gelatinizes the resin composition. The plasticimpression compoitions of the invention therefore include a solventsystem which is capable of forming with the solid resin a deformable orplastic impression taking gel. During this stage, the composition is anelastomeric mass. The solvent system and the resin composition may bemixed in various ratios which are easily determinable by practitioners.In the practice of the present invention, the solvent system includesextenders like secondary plasticizers, such as the alkyl arylhydrocarbons; fixed, edible vegetable oils, and the like, to providecontrolled setting time and non-tackiness. The solvent system mayinclude other additives which may be coupling agents to preventseparation of the extender, cohesion adjuvants to enhance or improve thecohesiveness of the plastic composition following the setting stage, andprimary plasticizers which flexibilize the composition as well as actingas coupling agents.-

In general, when the resin composition and the solvent system are mixed,the mixture passes through transient viscosity stages which include aninitial wetting stage wherein the solid resin is totally wetted with thesolvent system; a following plastic or impression taking or mold makingstage during which the non-tacky mixture can be shaped or molded intodesired contours (during this impression taking stage, the plasticimpression material may be considered as being in a condition where thedissolution of the polymer in the solvent system is only partiallycompleted); and a later molding stage, wherein the limited solvation iscompleted and the mixture may be considered as having reachedessentially equilibrium conditions which are characteristic of the gelforms of these compositions. This gel-like formation is a preliminarystep to the set of a later stage of the plastic impression material. Ifthe gel forms and sets in the ear, for example, it forms in a solidelastomeric mass which takes an accurate reproduction or impression ofthe ear canal, and this impression is dimensionally stable for thepurposes of this invention. After this set stage, the mold forming orimpression taking property of the composition is no longer present. Theset elastomeric or elastic material is also referred to as an elasticimpression material.

The solvent system is used to advantage because it contains a benzylradical containing compound which is liquid at room temperature. Theseinclude the benzyl alcohols, benzyl aldehydes, benzyl chlorides, benzylketones, benzyl ethers, benzyl amines, benyl cyanides and benzyl esters.These benzyl radical compounds have been discovered to be solvent gelformers. It has further been found that room temperature aliphaticliquid esters of the benzoic acids and the salicylic acids are alsooperable gel forming solvents for the purposes of this invention, amongwhich may be mentioned alkyl benzoate and alkyl salicylate. Among theoperable room temperature liquid gel formers are benzyl alcohol and itsderivatives, benzyl benzoate, benzyl acetate, benzyl butyrate, benzyl,formate, benzyl propionate, benzyl salicylate, dibenzyl ether, phenylmethyl carbinol, benzyl isoamyl ether, phenyl ethyl alcohol, methoxybenzyl alcohol (anisic alcohol), phenyl propyl alcohol, phenyl ethylisobutyrate (benzyl carbinol isobutyrate), dimethyl benzyl carbinol,benzyl phenyl acetate, phenyl ethyl butyrate, dibenzyl ketone, phenylethyl isovalerate, benzyl acetaldehyde (phenyl propyl aldehyde), phenylethyl benzoate (benzyl carbinil benzoate), benzyl ethanol amine, benzylthiol, benzyl butyl ether, methyl benzyl ether, benzyl cinnamate, andthe like.

It has been found that the benzyl radical gel former need comprise onlya minor portion of the solvent system, say about from 10% up to about50% by volume of the liquid component. It has also been found that theliquid component should contain an extender which may be a secondaryplasticizer such as an aryl alkyl hydrocarbon oil, or a fixed ediblevegetable oil, or both. Other extenders may be used, such as anaphthenic oil. The petroleum oil extenders are more economical than thevegetable oils. The hydrocarbon petroleum oil extenders have nosolvating powers, and they include Jayflex 205 supplied by the EnjayChemical Co., Mobilsol L supplied by the Mobil Oil Company, Shell-Flexsupplied by the Shell Oil Company and others. The use of the oilextenders leads to several advantages, namely, they extend the reactiontime to a desired control level to attain adequate handling and moldingtime before the composition sets, while still realizing a relativelyquick set of less than about one hour. The oil extender further leads toeconomies in using the resin component. Another important feature of theoil extenders is detackification, that is, they impart anti-tackiness tothe plastic composition which is desirable when the compositions arebrought into contact with dry tissue surfaces.

On occasion, the alkyl aryl hydrocarbon oils may be partly incompatibleand separate or sweat out from the composition because such oils may notmix with ingredients such as benzyl alcohol or glycol diacetate. Thisdoes not necessarily blunt the successful practice of the invention, andsuch separation may be reduced or eliminated by adding coupling agentsto the liquid component. It has been found that some benzyl alcohols,butyl benzoates and liquid alkyl phenols such as amyl phenol and nonylphenol operate as coupling agents as well as solvents, gel formers, andflexibilizers. Other coupling agents are not solvents, such as hexadecylalcohol, and other higher alcohols. Primary plasticizers such asdibutylphthalate have very slow solvent properties at room tempearture,but they are usefully added as coupling agents and flexibilizers.Smaller amounts of the primary plasticizers do contribute some solvationat room temperature, and further impart the property of flexibility,that is, they improve the plastic handling of the composition. Thesolvent type coupling agents are preferred even though they may lead tosome tackiness. In particular, it has been found that the alkyl phenolsvery successfully prevent separation of the alkyl aryl hydrocarbon oilswhen benzyl alcohol, and the like is present in the solvent system.

The alkyl aryl hydrocarbon oils are recognized secondary plasticizes,that is, extenders for primary plasticizers. Their essentialcharacteristic is that of a diluent rather than as a solvent. Thepreferred alkyl aryl hydrocarbons are oily liquids of a substantiallyclear color, and substantially free of objectionable odor. They have amolecular weight range of between about 240-320. The alkyl arylhydrocarbon may be an aromatic, such as toluene, alkylated with analiphatic compound, such as propylene, as taught in U.S. 3,211,690. Thealkyl aryl hydrocarbon may also be a petroleum fraction having a majoramount of a saturated hydrocarbon such as a parafiin or a cycloparafiin,and a minor amount of an aromatic hydrocarbon.

One such alkyl aryl hydrocarbon is known as Jayflex 205 and is suppliedby the Enjay Chemical Co. Jayflex 205 has about 88% of saturatedhydrocarbons of which about 6% is a paraffin and the balance isnaphthene. The aromatic portion is present in about 12% by weight ofwhich less than one-half is of a one ring benzene type and the balanceis of different types of indenes. Another alkyl aryl hydrocarbon isknown as Elastex 88-S and is supplied by Allied Chemical Corporation.The alkyl aryl hydrocarbons which are particularly useful as extendershave a generally clear color, no objectionable odor, have relatively lowspecific gravities of from 0.86 to about 0.88, and have a boiling range(-95%) of in excess of 500 R, up to about 700 F.

The edible, fixed vegetable oils which are useful as extenders includesafflower oil, linseed oil, cottonseed oil, corn oil, sunflower oil,rape oil, peanut oil, and soybean oil. Such oils also impart lubricity,have the property of detackification nad desirably extend the reactionor molding time before the composition set into an elastomeric mass. Thevegetable oils are compatible or miscible with the benzyl compound,whereas the petroleum oil extenders generally are not. It has beenfurther found that mirtures of vegetable and petroleum oils tend toprevent separation, even without a coupling agent. Coupling agents inamounts suflicient to prevent separation, however, are preferred asincluded ingredients.

The plastic composition may also include a minor amount of a cohesionadjuvant to enhance the cohesive properties of the composition duringthe handling in taking a mold impression and removing a set elastomericmass from contact with an anatomical pattern or the like. Such cohesionadjuvants are preferably tris ,8 chloroethyl phosphate, partiallyhydrogenated terphenyls and primary phthalate plasticizers such as butylbenzyl phthlate. Others may also be operable to serve this feature ofthe invention.

The solid component includes one or more resins. It is preferred toinclude a low molecular weight methacrylate polymer or copolymer insmall bead or granular form. Useful methacrylate polymers are ethylmethacrylate and isobutyl methacrylate, but a copolymer may be used withlike success, such copolymer being the product of ethylmethacrylate andbutylmethacrylate. Other resins may be included in the solid componentssuch as an ethylene derived resin, namely, vinylchloride,vinylacetatevinylchloride copolymers and the like. It has been foundthat the solid components may be more successfully manipulated if aminor amount of an anti-tack solid or powder is added to the solidcomponent, such anti-track powders include calcium carbonate, ultrafinesilica, zinc stearate and the like.

Oter gel formers may be added to the liquid component which bythemselves would be inadequate or possess disadvantages. Such gelformers are compounds containing both alcohol and other groups, slowevaporating esters, higher molecular weight glycols, and benzyl radicalcontaining plasticizers.

The liquid components are formulated so that the oil extenders compriseabout 20% to about 65% by volume of the liquid component. In general,greater amounts provide more lubricity and dilution, which also extendsthe reaction or setting time. It is therefore preferred not to addextenders in excess of 45% by volume of the liquid component in mostapplications. The balance of liquid components may include the benzylcompound gel formers or solvents and the coupling agents. Of thebalance, the major amount comprises the benzyl compound solvent, and theminor amount being the coupling agent. The liquid component preferablycontains a primary plasticizer such as dibutyl phthalate, benzyl butylphthalate, or the like, in small amounts of from about 5% by volume toabout 30% by volume. The primary plasticizers impart flexibility orresiliency, and further impart cohesiveness to the composition. Cohesionadjuvants may also be added to enhance the cohesive properties of thecomposition,

particularly after a primary plasticizer is added. Such a cohesionadjuvant may be added up to about 5% by volume of the liquid component.

It will be noted that some benzyl containing compounds lead to desiredproperties of cohesiveness and flexibility without requiring inclusionof a conventional primary plasticizer. Among such benzyl compounds areesters such as benzyl phenyl acetate, butyl benzoate, benzyl acetate,and others.

The relative amounts of liquid and solid components are not critical andgenerally enough liquid component should be used to easily wet theamount of solid components that are employed. Suflicient liquidcomponent should be added to a given amount of solid so the resultingmixture has a soft plastic consistency with sufiicient flow to providegood details and good handling when the soft plastic mixture is broughtinto contact with the par ticular anatomical structure. In general, fromabout 5 cc. to about 12 cc. of liquid component may be mixed with about10 grams of the solid component, but this may be varied by thepractitioner who will readily perceive when a sufiicient amount ofliquid component is added to obtain the desired soft plastic consistencyand handling. While the benzyl radical compounds, which are liquids atroom temperature, operate within the scope of the invention, it ispreferred to employ benzyl alcohols as the solvent gel former. Linearstraight chain alcohols, as such, are not all operable and many of thempresent problems even when they attain various degrees of operability.,

Linear primary alcohols having chains of 10 or more carbon atoms do notact as solvent gel formers with the polymers used in this invention.Benzyl alcohol has excellent properties in addition to its dispersingand gel forming attributes. Benzyl alcohol is a surface anesthetic andantiseptic, and these properties are decided advantages for plasticimpression materials intended to be used in contact with variousanatomical structures. The benzyl alcohols are additionally high boilingmaterials and have low water vapor transmissions or vapor pressures.This permits the plastic impressions, which include the benzyl alcoholsand the like, to be dimensionally stable at room temperatures even whenthe impression molds have thin cross-sections. The benzyl alcohol doesnot rapidly leave the plastic impression by evaporation or other loss toadversely affect the dimensional stability. The benzyl alcohols arehydrophobic, therefore, they do not dehydrate human tissues, they arenon-irritating to tissues, they have a very low order of toxicity, theyare all resistant to fungal attacks, and they have a pleasant odor.

The following examples are presented to teach various advantages andembodiments of the present invention, but it should be understood thatthe disclosed embodiments are intended to be only illustrative.

EXAMPLE 1.

A number of plastic gel forming materials were prepared by mixing 2grams of a solid ethyl methacrylate powder with 1.5 cc. of thirty threevarious solvent gel formers. The setting time was recorded for eachplastic composition, that is, the time when the gel loses its tackiness.

Solvent: Time Benzyl chloride 1'30" Benzyl cyanide 2'30" Benzyl formate2'30" Benzyl alcohol 2'30" Benzyl thiol 2'30" Benzyl acetate 3' Phenylmethyl carbinol 4' Benzyl iso amyl ether 5' Benzyl propionate 7' Phenylethyl alcohol 8' Benzyl butyrate 9' Anisic alcohol 10' Phenyl propylalcohol 11 Solvent: Time Benzyl carbinol isobutyrate l3 Dimethyl benzylcarbinol 14' Dibenzyl ether Benzyl phenyl acetate Dibenzyl ketone Benzylacetaldehyde Benzyl n-butyl ether 16' Methyl o-chlorobenzoate 15Cinnamic aldehyde 15 u-Propyl benzyl alcohol 20' Phenyl ethylmethylethyl carbinol 20 p-Isopropyl benzyl alcohol 35' Benzyl benzoateBenzyl salicylate Methyl benzyl ether 1 hr., 40 Benzyl cinnamate 2 hrs,30" Ethanol 1'30 Isopropanol 13' Decyl alcohol No gel C12C13 alcohols NOgel Hexadecyl alcohol No gel The foregoing shows that all the benzylcontaining compounds are gel formers with the solid resin component.Substantially all of the benzyl compounds exhibit preferably shortersetting times of under one hour. Those gel formers which have longersetting times, say above about 10 minutes, may be combined with theshorter setting time gel formers to reduce their setting time. Thesetting time may therefore be tailored in this respect to meetparticular requirements of a given plastic impression composition.

Benzyl alcohol does not have the disadvantage of fast evaporation whichwould make it undesirable for use in plastic impression materials. Therelative evaporation rates of benzyl alcohol and some other solvents orgel formers are seen from the following list of vapor pressures measuredin mm. of mercury.

Solvent C. Mm. Hg

Ethanol 20 44 Isopropanol 20 33 Methyl benzyl alcohol 20 0. 01 Glycoldiacetate 0. 3 Benzaldehyde. 1 Benzyl alcohol--. 1 Benzyl amine 29 1Phenyl ethyl alcohol. 58. 2 1 Benzyl ethyl ether- 26 1 n-Butyl benzoate20 0. 13 Hexylene glycol 20 0. 05 oz-Methyl benzylether 20 0. 01a-Methyl benzyl mcnoethanol amine 20 0. 01

Ethyl alcohol has the disadvantage of a too rapid setting time and a toorapid rate of evaporation for successful handling. Consequently, thedimensional stability of the set product is adversely affected.

EXAMPLE 2 A solid resin component is prepared from the followingmaterials and amounts.

Material Amount Ethylmethacrylate polymer 90 lbs.Vinylchloride-vinylacetate copolymer 11 lbs., 9 oz. Zinc stearate 6lbs., 5 oz.

The above materials are mixed for 1 hour. The vinyl resins operate asextenders for the solid resin compositions, that is, themethacrylatepolymer. The zinc stearate operates as an anti-tack additive.

The examples of the following Table *I show various solvent stystemswhich are prepared by mixing volumes of the listed ingredients. Aplastic composition is prepared in each instance by combining 8 grams ofthe solid resin component of Example 2 with 5 cc. of a liquid componentwhich represents the following solvent systems. The alkyl arylhydrocarbon ingredients is Jayflex 20 5, and the edible vegetable oilingredient is corn oil.

Components, cc.

Ingredient 1 2 3 4 5 6 7 8 Alkyl aryl hydrocarbon.-. 15 15 5 15 20Plienyl methyl carbinol 15 Phenyl ethyl isobutyrate 15 Benzyl cyanide l5Bcnzylpropiouate 15 Benzyl phenyl acetate Dibenzyl ether Dibenzyl ketonePhenyl ethyl alcohol Sec. amyl phenol. Butyl benzoate Benzyl ethanolamine Benzyl acetate Butyl benzoate Phenyl propyl a dehyde 15 Phenylethyl benzoate 15 Phenyl ethyl isobntyrate 10 Benzyl alcohol 10 Dibntylsebecate. Butyl benzyl phthalate Anisio alcohol Dibutyl phthalatcDinonyl phenol Gelling time, minutes. Setting time, minutesBenzylalcohol 20 50 28 30.3 30.3 50 10 Alkylarylhydrocarhon. 22 50 30.633.5 33.5

Butyl benzoa Ethyl glycol Glycol diacetate Dibutyl phthalate. Hexo deeylalcohol* Hexylene glycol Ethoxylated lauryl alcohol" 36. 2 Ediblevegetable oil 50 18 Benzyl benzoate Benzyl salicylate. Gelling time,minutes. Setting time, minutes 8 4 6 8 TABLE II Liquid components, partsby volume Ingredient A B C D E F Benzyl alcohol 10 10 1O 1O 10 10Dibutylphthalate 10 5 5 5 (Enjay 205) alkyl aryl hydrocarb 10 5 5Safllower oil 10 5 5 Component A is a miscible mixture of the benzylcompound and the primary plasticizer, which sets quickly but which isvery tacky, and not moldable for that reason. Component B sets quicklyunder controlled molding time but there is some separation ofingredients and the composition has little cohesion. Component C is amiscible mixture of the benzyl compound and a vegetable oil which setsquickly, is non-tacky, but does not have the desired cohesion. Theplastic composition, however, is useful as a plastic impressionmaterial, especially for some applications. Component D sets quickly andhas good cohesiveness, but there is some separation because the primaryplasticizer is present in an insufficient amount. Component E sets tooquickly and is not moldable after 2 minutes. This is due to the slightlower amount of extenders which, however, are sufficient to detackifythe composition. This composition is not sufficiently cohesive and pullsapart, as a result of the somewhat lower amount of primary plasticizer.Component F leads to a moldable composition of good cohesiveness whichsets quickly, and in which the ingredients do not separate. The fixedvegetable oil appears to cooperate with the primary plasticizer tooperate as a coupling agent, apparently because of the miscibility withthe benzyl compound.

EXAMPLE 4 A liquid component of a primary plasticizer in a volume of cc.was mixed at room temperature with grms. of the solid resin of Example2. Each plastic composition required from 4 to 10 hours to set. Theprimary plasticizers used in the various liquid components were:

Tricresyl phosphate Tris-B-chloroethyl phosphate Dibutyl phthalate Butylbenzyl phthalate Dipropylene glycol dibenzoate Methyl phthalyl ethylglycolate Each plastic composition required from 4 to 10 hours to set.All the foregoing primary plasticizers are therefore inadequate tocomprise a useful solvent system as such for the plastic impressioncomposition in accordance with the purposes of the present invention.

EXAMPLE 5 A plastic composition of 10 grrns. of the solid component ofExample 2 mixed with 5 cc. of benzyl alcohol set in less than 3 minutes.When a liquid component of 5 cc. benzyl alcohol plus 5 cc. of cottonseedoil is mixed with 10 grms. of the same solid component the setting timeis extended to about 8 minutes.

EXAMPLE 6 Ingredient Parts by volume Benzyl alcohol 33 Dibutyl phthalate37 Al-kyl aryl hydrocarbon (Enjay 205) l5 Safilower oil 12 Cohesionadjuvant, tris-B-chloroethylphosphate 3 The above liquid component isused in mixture with the solid resin component of Example 2, on thebasis of 10 grmsl of solid component of 5 cc. of liquid component. Themixture gels within 1 minute and sets within 8 minutes to an elastomericmass which is non-tacky and which has good cohesiveness. A mold of anouter ear canal is formed with good definition, with ease during the 4minute period before setting.

The plastic impression compositions which are prepared with solventssuch as benzyl alcohol and oil extenders provide easy handling withcontrolled setting times, they are not tacky, they are desirably plasticduring the early viscosity stages for sufiicient times to takeimpression, they develop a set plastic body which is still elastic, theyare dimensionally stable over long periods, they produce no irritationor discomfort to the subject, they do not develop exothermic heat at anyviscosity stage, they generally are free from irritation to either thehands of the manipulator or the ear of the subject, and they have apleasant natural odor. The plastic impression materials of thisinvention have, in addition, economic advantages because the impressioncan be quickly and simply 10 retaken in case of an apparent defect.Also, the plastic impression can, be withdrawn from the investment flaskintact in preparing the plaster or stone molds. In this way, the finallymolded product can be visually compared with the impression materialwhich was used to make the mold.

The invention may now be practiced in the various ways which will occurto practitioners, and such practice will be a part of the invention solong as it comes within the terms of the following claims as givenfurther meaning by the language of the preceding specification.

What is claimed is:

1. A plastic composition to take an elastomeric impression, comprising:

a thermoplastic granular loweralkyl methacrylate copolymer,

a room temperature gel forming solvent system for said resin to form aplastic impression taking gel within about one hour, which solventsystem includes from about 10 to about 50 percent by volume of benzylalcohol, said solvent system being further present from about 5 to about12 cc. per 10 grams of said resin, and

an oil extender selected from the class of alkyl aryl hydrocarbonsecondary plasticizers and fixed edible vegetable oils, said oilextender being in said solvent system from about 20 percent to about 65percent by volume.

2.. A plastic composition as in claim 1 wherein said solvent systemcontains from about 5 percent to about 30 percent by volume of aplasticizer to flexibilize the plastic composition.

'3. A plastic composition as in claim 1 wherein said solvent systemcontains less than about 20 percent by volume of a primary phthalateplasticizer.

4. A plastic composition as in claim 1 wherein said solvent systemcontains less than about 20 percent by volume of a primary phthalateplasticizer, and wherein said oil extender is a secondary alkyl arylhydrocarbon plasticizer substantially clear and free of odor, and havinga specific gravity from about 0.8 6 to about 0.8-8, comprising a mixtureof paraflin and aromatic compounds, and a boiling range in excess of 500F.

5. A plasticcomposition as in claim 1 wherein said solvent systemconsists essentially of said benzyl alcohol and a fixed edible vegetableoil.

6. A plastic composition as in claim 1 wherein said solvent systemconsists essentially of said benzyl alcohol and an alkyl arylhydrocarbon secondary plasticizer.

References Cited UNITED STATES PATENTS 2,885,378 5/1959 Darby 260-3182,934,510 4/1960 Crissey et a1 260-31.'8 3,152,096 10/1964 Darby 26030.43,211,689 10/1965 Darby 2603l.4

OTHER REFERENCES Buttrey, Rlasticizers, Cleaver-Hume Press Ltd., 2nded., 1958, pp. and 192.

ALLAN LIEEBRMAN, Primary Examiner L. T. JACOBS, Assistant Examiner US.Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent N0 DatedJanuary 26,

Inventor(s) Eugene J. Molnar It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

In the heading to the printed specification, after 1i] 4, insertAssignor to Coe Laboratories, Inc., Alsip,

111., a corporation of Illinois Signed and sealed this 16th day of May1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissionerof Patents

